The kelly and swivel was on the drill pipe when this loss of control occurred. The Hydrill did not close because the flow was clearly annular, around the kelly and up against the floor and rotary table slot, or key, whatever you want to call it. The flow was great enough to blow the KB out of the table, then the table itself out of the key and up thru the drilling rig floor. The rotary table and kelly bushing were both badly flow cut.
When stuff happens it happens fast and with a level of energy and force that will often surprise the hell out of you. Sometimes all you can do is just stand back and mumble holy shit to yourself. But you better get over that quickly and start figuring out how to solve the problem.
With the kelly on the hole the well was pumped dead with mud.
All's well that ends well.